A flexible wiring board has good flexing characteristics and thus has heretofore been used in the wiring of electric apparatus and electronic apparatus, particularly in the wiring of mobile members in computer peripheral such as HDD and CD-ROM.
Such a flexible wiring board is prepared, e.g., by laminating a conductor layer such as metal foil on an insulation layer such as plastic film optionally with an adhesive layer of synthetic resin or the like provided interposed therebetween, subjecting the conductor layer to etching or other treatments to form a predetermined circuit pattern thereon, and then laminating an insulation layer on the conductor layer optionally with an adhesive layer provided interposed therebetween.
In recent years, with the enhancement of the performance and improvement in the mobility of electric apparatus and electronic apparatus, particularly computer peripheral, the internal temperature in these apparatus tends to rise more and more. It has thus been desired to develop a flexible wiring board which exhibits a sufficient flex life under working conditions causing such a temperature rise.